Torsional vibration damper

ABSTRACT

A rotary coupling device has a hub driving a hub flange formed with windows containing helical compression springs. Those springs are also contained in windows in disc-like side plates rivetted together to form a carrier for friction material. The springs are also contained in windows respectively in floating disc-like plates. The windows are so dimensioned that an initial relative rotation between the friction material carrier and the hub and hub flange, causes one of the springs to be compressed and urge the floating plates to rotate relatively to the carrier or to the hub and hub flange so that the relative movement between the floating plates and the carrier or the hub and hub flange compreses the other of the springs. Thus during this initial movement the springs are compressed in series. Once the relative rotation between the carrier and the hub and hub flange exceeds a certain angle, the plates no longer take part in the compression of the springs which are now compressed in parallel between the carrier and the hub and hub flange.

This invention relates to a torsional vibration damper and moreparticularly to a rotary coupling device comprising the damper to dampout torsional or rotary vibrations superimposed on a rotary motion inputto the coupling so that a rotary motion output from the coupling may befree of said vibrations or at least they may be reduced.

The rotary coupling device is of a type (hereinafter called the "typereferred to") intended for rotation about an axis and comprising a firstcomponent part and a second component part each rotatable about the axisand also capable of a rotation one relative to another about said axis,a plurality of compression spring means disposed between the first andsecond component parts, said spring means being capable of transmittingrotary motion from one said component part to the other, and each saidspring means being compressible along a circumferential direction (withrespect to the rotation about said axis) by relative rotary movementbetween said first and second component parts.

Each spring means can be of any suitable, compressible, elasticallydeformable kind, for example a helical spring or a rubber cushion.

One example of a coupling device of the type referred to is a drivenplate for a friction clutch. In the driven plate one said component partis formed by an annular array of friction material on a disc-likecarrier plate and the other said component part is a disc-like flangeaxially spaced from the carrier plate. That flange either has a centralaperture lined with axial splines or is rotationally fast with a hollowhub lined internally by axial splines, said splines being to mesh withaxial splines on a shaft. The carrier plate and flange each have windowscontaining said spring means. The driven plate is included in a clutchprovided with a pressure plate arranged to releasably clamp the drivenplate against a rotatably driven counter-pressure plate. Thatcounter-pressure plate may be driven by an engine of a motor vehicle andcan be the fly-wheel of the engine. Therefore said shaft may be an inputshaft to a gearbox in a transmission of the vehicle.

Another example of a coupling device of the type referred to is adivided or split fly-wheel in which said first component part is a firstfly-wheel arrangement axially spaced from the second component partformed by a second fly-wheel arrangement, the two fly-wheel arrangementsbeing interconnected using said plurality of spring means. A splitfly-wheel as aforedescribed may be used as a fly-wheel of a motorvehicle engine. One of said fly-wheel arrangements can form acounter-pressure plate of a clutch whilst the initial rotary drive isinput to the other fly-wheel arrangement. An example of such a splitfly-wheel is described in published British Patent Application GB 2166220 A.

In known coupling devices of the type referred to, the relative rotationbetween said first and second components is a function of the rates ofthe respective spring means and the value of the driving input torqueapplied to one of said first or second components when the othercomponent experiences retardation caused by inertia and friction Oftenthe various spring means are arranged so that one or more have lowspring rates and one or more have higher rates. The arrangement is thatthe spring means are staggered so that the initial relative rotarymovement between the first and second components compresses the lowrated spring means until the torque input reaches a value where the lowrated spring means have allowed a sufficient relative movement betweenthe first and second components, that the respective higher rated springmean start to be compressed.

An object of the invention is to provide a coupling device of the typereferred to capable of being constructed to increase the input torquerange over which lower spring rate torsional vibration damping isavailable.

According to the invention, there is provided a rotary coupling deviceof the type referred wherein there are at least first and second saidspring means so arranged that during an initial part of said relativerotary movement the first and second spring means are compressed in aseries relation in which the compression of each of the first and secondspring means is only a fraction of the accomplished relative rotarymovement between the first and second component parts, and during alater stage of the relative rotary movement said first and second springmeans are compressed in a parallel relation.

An advantage is that low rate spring damping over an extended initialrange of torque input can be achieved without the need to useexcessively long weak springs to provide a first damping stage as wouldbe the case if the weak first stage damping over an extended torquerange were achieved by first and second spring means compressed inparallel. Also, during the first stage of damping, the actualcompression of each the first and second spring means can beconsiderably less than the relative rotary movement (deflection) betweenthe first and second component parts to achieve that compression. Thisreduction in compression for a given deflection can extend the life ofthe spring means.

The invention will now be further described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a cross-section of a driven plate formed according to theinvention, for a friction clutch; FIG. 1 additionally showsdiagrammatically a driven counter-pressure plate and also a fragment ofa diaphragm spring being part and representative of a friction clutchcover assembly;

FIG. 2 is a side view of a hub flange for the driven plate in FIG. 1;the hub flange being shown, in relation to stop pins, when the hubflange and side plates and a floating disc in the driven plate are in astart or "central" position for example, when a clutch comprising thedriven plate is fully disengaged and there is no torque input to thedriven plate;

FIG. 3 is a side view of a said floating disc for the driven plate inFIG. 1, the floating disc being in the "central" position;

FIG. 4 is a side view of a said side plate and illustrates arelationship between windows (containing helical springs) in the sideplate, in the hub flange, and in a said floating disc of the drivenplate in FIG. 1 when in the "central" position;

FIG. 5 is a diagrammatic view representing a fragment of FIG. 4 when thedriven plate is in the "central" position, this view correlating FIG. 4with following FIGS. 6 to 11;

FIGS. 6 to 8 diagrammatically illustrate a drive condition of the drivenplate represented by FIGS. 4 and 5; in this drive condition the clutchis engaged and torque is input to the driven plate from thecounter-pressure plate, FIG. 6 showing a situation during first stagedamping, FIG. 7 showing the end of the first stage, and FIG. 8 showingsecond stage damping;

FIGS. 9 to 11 diagrammatically illustrate an over-drive condition of thedriven plate represented by FIGS. 4 and 5; in this over-drive conditionthe clutch is engaged and torque is input to the driven plate through ahub thereof, FIG. 9 showing a situation during first stage damping, FIG.10 showing the end of that first stage, and FIG. 11 showing second stagedamping, and

FIG. 12 shows a graph representing variation in relative angularmovement M° (in angular degrees) between hub flange 28 and carrierassembly 18, 16, 18A with variation in torque input T at drive D andover-drive O-D in a clutch provided with the driven plate in FIG. 1 in amotor vehicle.

With reference to FIG. 1 a clutch is illustrated diagrammatically by:

(i) a rotatably driven counter-pressure plate 2, for example afly-wheel, which could be driven by an engine of a motor vehicle;

(ii) a clutch driven plate 4; and

(iii) a clutch cover assembly represented by fragments of a diaphragmspring 6 and a fulcrum ring 8, the cover assembly further comprising aknown cover (not shown) secured to be fast in rotation with thefly-wheel, an axially movable known pressure plate (not shown) withinthe cover and fast in rotation therewith, and the diaphragm springacting between the cover and pressure plate to urge the latter to clampthe driven plate 4 against the counter-pressure plate 2.

The driven plate 4 has a central hub 10 for rotation about axis X. Thehub bore is lined by axial splines 12 intended to engage in known mannerwith external axial splines on a rotatable shaft (not shown), forexample an input shaft to a gearbox which could be in a transmissionline of a motor vehicle.

Driven plate 4 has annularly arrayed friction material 13 secured to acarrier ring 14 which may include known metal, cushioning segments. Ring14 is rivetted by axial stop rivets 16 to a disc-like side plate 18surrounding the hub 10 and alongside an annular, radial rib 20 on thehub. Also secured to the stop rivets 16 is another disc-like side plate18A axially spaced from the plate 18 so that there is formed a one-piececarrier assembly 18, 16, 18A for the friction material 13 and capable ofrotating, relatively to the hub 10, about axis X.

Part of the rib 20 is formed with axial extending splines 24 engagingwith axial splines 26 around the inner periphery of a disc-like hubflange 28 (see FIG. 2). In its outer periphery the hub flange 28 hasfour substantially similar notches 30 through which the stop rivetts 16pass so that a relative rotary movement between the hub flange 28 andthe carrier assembly 18, 16, 18A is limited by the circumferential orangular length of each notch. When the hub flange 28 is in the "central"position each stop rivet is A° (that is A angular degrees) from one endof the respective notch 30 and B° from the other end. When the drivenplate is in drive condition the maximum relative movement permittedbetween the hub flange 28 and carrier assembly 18, 16, 18A from thecentral position is A°, whilst in over-drive condition the maximumpermitted relative movement is B°.

The hub flange 28 (see FIG. 2) has four windows 281 and 282. All thesewindows have substantially the same radial width. Circumferentially,both diametrically opposed windows 281 have the same length. Also bothdiametrically opposed windows 282 have the same circumferential length,but each window 281 is circumferentially shorter than each window 282.Each of the notches 30 is diametrically opposite another notch 30. Allthe windows 281 and 282 are substantially equi-spaced one from anotherand each window is substantially equi-spaced from the notches 30adjacent thereto. Therefore, the angular spacing C between the notches30 in one set of two adjacent notches is less than the angular spacing Ebetween the notches in another set of two adjacent notches.

In each of the two side plates 18 and 18A there is a similar array ofwindows, each window in one side plate being directly opposite a similarwindow in the other side plate. Therefore the nature of the windows inboth side plates 18 and 18A can be conveniently described with referenceto the side plate 18 in FIG. 4 which has four windows 181 and 182. Thetwo diametrically opposed windows 181 have substantially the samecircumferential length. Also the two diametrically opposed windows 182have the same circumferential length but it is greater than that of eachof the windows 181. All the windows 181, 182 are substantiallyequi-angularly spaced apart one from another.

Two floating disc-like plates 32 and 32A between the side plates 18 and18A are disposed to either side of the hub flange 28. Relative rotarymovement can take place between the floating plates 32, 32A and the sideplates 18, 18A and between the floating plates and the hub flange 28.The arrangement of peripheral notches and windows is the same in bothfloating plates 32 and 32A and therefore will be conveniently describedwith reference to FIG. 3 showing the plate 32. In that floating platethere are four similar peripheral notches 34, each two opposite notches34 being diametrically opposed, and each notch extending over the sameangular distance or circumferential length as the notches 30 (FIG. 2);in which case a° (FIG. 3) equals A° (FIG. 2) and b° (FIG. 3) equals B°(FIG. 2). There are also the angular spaces C or E between adjacentnotches 34 as there are between the notches 30 (FIG. 2) as describedabove. If desired the notches 34 may be of a different circumferentiallength to the notches 30. Side plate 32 has four similar windows 321 and322 therein, all of these windows extending over the same angulardistance or circumferential length. The four windows can form four setsof two adjacent windows 321 and 322. In two opposed sets, the twowindows in each set are spaced by the same angular distance F. In theother two opposed sets, the two windows are spaced by the same angulardistance G which is less than F. Referring to FIGS. 1 & 4, each of thesets of windows aligned in the axial direction of the driven platecontain a respective helical compression spring 36. All the springs 36are of substantially the same rate in this example (though they could beof differing rates) and of substantially the same initial unstressedlength (though they could be of differing unstressed lengths), and whenconstrained in their respective sets of windows each spring is ofsubstantially the same constrained length when the drive plate is in the"central" position. If desired the windows may be shaped and disposed sothat in the "central" position of the driven plate at least one of thesprings 34 has a constrained length which differs from the constrainedlength of another of the springs 34 With reference to FIG. 4, when thedriven plate 4 (FIG. 1) is in the clutch for connecting the engine withthe transmission of a motor vehicle, the driven plate is rotated indirection H during forward running of the vehicle. In that case it willbe seen that all the windows 181, 281 and 321 have respective leadingedges 1811, 2811 and 3211, and that all the windows 182, 282 and 322have respective trailing edges 1822, 2822 and 3222. In each of the twosets of axially aligned windows comprising a said window 181 then, inthe "central" position, the leading edge 2811 of the hub flange window281 is circumferentially spaced from the leading edges 3211 of the twofloating plates windows 321 by an angular distance J, and the leadingedges 3211 are circumferentially spaced by an angular distance K fromthe leading edges 1811 of the windows 181 of the two side plates;whereas the trailing edges of the windows in each of those two sets arein coincidence. In each of the two sets of axially aligned windowscomprising a said window 182 then, in the "central" position, thetrailing edges 1822 of the side plates windows 182 are circumferentiallyspaced from the trailing edges 3222 of the two floating plates windows322 by the angular distance J, and the trailing edges 3222 arecircumferentially spaced by the angular distance K from the trailingedge 2822 of the window 282 of the hub flange; whereas the leading edgesof the windows in each of those two sets are in coincidence. The angularvalue J represents the angle of the relative rotation between the hubflange 28 and the floating plates 32, 32A that must be accomplished tobring into substantial coincidence the leading edges 2811 and 3211 atthe respective set of windows having those edges, and simultaneously tobring into substantial coincidence the trailing edges 1822 and 3222 atthe respective set of windows having said edges 1822, 3222. The angularvalue K represents the angle of the relative rotation between the hubflange 28 and the floating plates 32, 32A that must be accomplished tobring into substantial coincidence the leading edges 1811 and 3211 atthe respective set of windows having those edges, and simultaneously tobring into substantial coincidence the trailing edges 2822 and 3222 atthe respective set of windows having said edges 2822, 3222.

The situation in FIG. 4 is also represented in FIG. 5 which onlyillustrates two sets of windows in alignment axially of the drivenplate. The code used to represent windows in FIG. 5 is used in FIGS. 6to 11, namely the side plates windows 181 and 182 are shown in fulllines, the hub flange windows 281 and 282 are in dotted lines, and thefloating plates windows 321 and 322 are in dash-dot lines; furthermore,for clarity the radial size of the windows 321 and 322 have been shownreduced in FIGS. 5 to 11 to distinguish them more from the windows 281and 282.

Returning to FIG. 1, the driven plate 4 is provided with an "idlingcentre" 40 for reducing the chance of an "idle rattle" in a transmissionline when the driven plate is used in a motor vehicle clutch. That"idling centre" is a weak torsional vibration damper comprising aplurality of weak auxilliary compression springs 42 in windows in adisc-like plate 44 and in a disc-like plate 46 which interacts with thewindows 281 and 282 in the hub flange 28 and is acted on by an annularspring 48. The "idling centre" 40 is described in our published BritishPatent Application No. GB 2131 914A and will not be described furthersince it is not essential to the present invention and may be omittedfrom the clutch driven plate if desired. But if the "idling centre" 40is used, then there will need to be some circumferential free playbetween the splines 24 and 26 (as described in GB 2131 914A). Thecomponents of the driven plate 4 are maintained together axially byC-clips 50 and 52 and the driven plate further comprises a wavy springwasher 54, and bearing rings or washers 56, 58 and 60 any of which canbe an hysteresis washer.

In the following description of operation, the driven plate 4 is in aclutch between the engine and transmission line in a motor vehicle. Theoperation will be particularly described with reference to FIGS. 5 to12, in which the two springs 36 in FIG. 4 are indicated at 36A and 36Bin FIGS. 5 to 11.

Starting with FIG. 5, the vehicle is stationary, the clutch comprisingthe driven plate 4 is disengaged, and the driven plate parts are in the"central" position. The clutch is then engaged and drive condition D(FIG. 12) commences by the engine applying input torque to the carrierassembly 18, 16, 18A (FIG. 1) which readily rotates in direction H withthe springs 36, the floating plates 32, 32A and the hub flange 28relatively to the hub 10 through the circumferential free-play betweenthe splines 24 and 26. This is the situation shown at OL in FIG. 12.When all that free-play is taken up, the carrier assembly, floatingplates, hub flange and springs 36 are still in the "central" position(FIG. 5). Continued application of an increasing torque input T (FIG.12) to the carrier assembly 18, 16, 18A (FIG. 1) now causes it to rotatein direction H relative to the hub flange 28. This is the situationshown in FIG. 6, where the movement of trailing end 1812 of the window181 of each side plate 18, 18A pushes the spring 36A against the leadingend 3211 of the window 321 of each floating plate 32, 32A in direction Hrelatively to the hub flange 28 causing the trailing end 3222 of thewindow 322 in each floating plate to push the spring 36B against leadingend 2821 of the window 282 of the hub flange. The compression of the twosprings 36A and 36B provides rotational damping during a first stage ofdamping represented by portion LN of the graph in FIG. 12. Throughoutthis first stage the springs 36A and 36B are compressed in series, theleading end of the spring 36A pushing via the floating plates 32, 32A onthe trailing end of the spring 36B. Whilst this series compression istaking place, the floating plates 32, 32A rotate relatively to the hub10 and hub flange 28 through an angle which is only substantially halfthe angle through which the side plates 18, 18A have rotated relativelyto the hub and hub flange. The end of the first damping stagecorresponding to point N in FIG. 12, is shown in FIG. 7. In thetransition from position L to position N in FIG. 12 during increasingtorque T input, the carrier assembly 18, 16, 18A has rotated, relativelyto the hub 10 and hub flange 28, through the angle 2J° (i.e. twice theangle J° of FIGS. 4 & 5). Therefore hub spring 36A and 36B is compressedby only half as much as if they would have been had they been subject toparallel compression between the side plates 18, 18A and hub flange 28without the floating plates 32, 32A being present, for a relativerotation between the side plates and the hub flange of J°. Although onlysprings 36A and 36B have been referred to, it will be understood thatthe other two springs 36 (FIG. 4) undergo similar compression as thesprings 36A and 36B in the operations shown in FIGS. 5 to 11.

The point N in FIG. 12 shows the end of the first stage of damping atdrive D condition. There is then a torque step (for reasons describedhereinafter) to point W which is the beginning of the second stage whichis performed between W and P. At the end of the first stage, (FIG. 7),the trailing end 1822 of the window 182 in each side plate now coincideswith the trailing end 3222 of the window 322 of each floating plate 32,32A whilst the leading end 2811 of the window 281 in the hub flange 28(FIG. 1) now coincides with the leading end 3211 of the window 321 ineach floating plate. Therefore, during second stage damping, all thesprings 36 (FIG. 5) are simultaneously compressed in parallel betweenthe trailing ends of the windows in the side plates 18, 18A (FIG. 1) andthe leading ends of the windows in the hub flange 28 as the carrierarrangement 18, 16, 18A continues to rotate relatively to the hub 10 andhub flange 28 in the direction H. A situation which occurs in the courseof the stiffer second damping stage is shown in FIG. 8. As the inputtorque T increases point P (FIG. 12) can be eventually reached where nomore second stage damping is available under drive D condition. Thisoccurs when the carrier arrangement 18, 16, 18A (FIG. 1) has rotatedthrough R° relatively to the hub flange 28 to bring the stop rivets 16into abutment with sides of the notches 30 (FIG. 2).

Starting again with FIG. 5 with the driven plate 4 in the "central"position, now if an over-drive O-D condition (FIG. 12) commences thetorque input to the clutch is applied to the hub 10 (FIG. 1) from thetransmission to drive the engine. Initially the hub 10 rotates readilyin direction H relatively to the hub flange 28, the springs 36 and thecarrier assembly 18, 16, 18A to take up the circumferential free-playbetween the splines 24 and 26. This is the situation shown at OQ in FIG.12. As the over-drive input torque increases a first damping stageoccurs (represented by section QS in FIG. 12) during which, as shown inFIG. 9, the springs 36A and 36B are compressed in series. This isbecause the hub flange 28 (FIG. 1) rotates in direction H relatively tothe side plates 18 and 18A and so the trailing end 2812 of the window281 of the hub flange presses the spring 36A against the leading end3211 of the window 321 in each floating plate 32, 32A. Therefore thetrailing end 3222 of the window 322 in each floating plate presses thespring 36B against the leading end 1821 of the window 182 in each sideplate 18 and 18A. The first stage ends (point S in FIG. 12) when theleading end 3211 of each window 321 in the floating plates 32, 32A comesinto coincidence with the leading end 1811 of each window 181 in theside plates 18, 18A so that spring 36A starts to press against eachleading end 1811 as shown in FIG. 10. At the same time the trailing end2822 of the window 282 in the hub flange 28 comes into coincidence withthe trailing end 3222 of the window 322 so that the trailing end 2822compresses the spring 36B against the leading ends 1821 of the window182 in each side plate 18, 18A. During the course of the first stage ofdamping in over-drive 0-D condition (FIG. 12), the hub 10 and hub flange28 rotate relatively to the carrier assembly 18, 16, 18A through theangle 2K° which is twice the angle K° through which floating plates 32and 32A have rotated relatively to the carrier assembly.

Should torque input in the over-drive direction continue to increasethen from point S (FIG. 12) there is a torque step (for reasonsdescribed hereinafter) to point Y and a stiffer second stage of dampingrepresented by the section YU in FIG. 12 occurs during which, as shownin FIG. 11 the springs 36A, 36B (all the springs 36 in FIG. 4) aresimultaneously compressed in parallel between the trailing ends of thewindows in the hub flange 28 (FIG. 1) and the leading ends of thewindows in the side plates 18 and 18A. As the over-drive input torqueincreases, point U can be eventually reached where no more damping isavailable due to the stop rivets 16 coming into abutment with sides ofthe notches 30 (FIG. 2) when the hub flange 28 has notched in directionH through V° relatively to the side plates 18 and 18A.

During the transition from first to second stage damping in either driveor over-drive conditions the torque step at WN or SY (FIG. 12) occurs.This is because during the first stage of damping the radially outermostcircumferential portion of each spring is compressed or nipped more thanthe radially innermost circumferential portion. This compressioncharacteristic which is maintained during the second stage of dampingaccentuates the sudden increased resistance to compression experiencedat the transition from series compression of the springs 36A, 36B toparallel compression. To reduce or eliminate the torque steps WN and SY(FIG. 12) and thus increase the chance of a smoother transition fromfirst to second stage damping, the aforesaid windows, for example in thehub flange 28 and floating side plates 32, 32A, can be shaped to ensurethat there is compression or loading of the springs 36 at their radiallyinnermost circumferential portions in the course of first and/or secondstage damping. An idea of how windows may be shaped to vary loading oftorsion springs is described in our European Patent Application No.EP.0073 594 A1.

In a modification, one of the floating side plates 32 or 32A can beomitted, however the side plates, hub flange and the remaining floatingplate should be held close together axially to prevent sloppiness.

It will also be understood that the use of one or more floating plates32, 32A or their equivalents, to enable torsional vibration damping tobe switched from first stage relatively weak damping by pairs ofcompression springs in which in each pair the two springs are compressedin series to second stage stiffer damping in which the two compressionsprings in each pair are compressed simultaneously in parallel, can beapplied to the torsional vibration damping in a divided or splitfly-wheel, which may be used in a motor vehicle.

Although the above description refers to first stage relatively weakdamping comprising compressing two springs in series and then in secondstage by compressing the two springs in parallel, the first stage maycomprise compressing three or more compression spring means in seriesand the second stage may comprise compressing two or more of thesespring means in parallel.

What is claimed is:
 1. A rotary coupling device comprising a hub havingan annular flange mounted thereon, a coaxial annular driven platemounted on the hub for limited rotational movement relative to the hubflange, a coaxial annular floating plate also mounted on the hub forlimited rotational movement relative to both the hub flange and thedriven plate, and at least two sets of spring means each housed in arespective set of aligned spring windows each spring window having twoopposed circumferential ends formed by respective window edges in thehub flange, the driven plate and the floating plate and which resist therelative rotational movement therebetween so that said spring meansdetermines an "at-rest" state when the driven plate is subject to noexternal torsional loads, wherein in each of said two sets of springwindows the hub flange window, the driven plate window and the floatingplate windows are of different circumferential lengths and are arrangedso that in the "at rest" state, for a first set of spring windows allthe window edges at one circumferential end of the respective windows insaid first set are in circumferential alignment, and for the second setof spring windows all the window edges of the respective windows in saidsecond set are in alignment at the the other of said two opposedcircumferential ends to said first set of windows, so that during aninitial phase of rotational movement of the driven plate relative to thehub flange the two spring means act in series and in a later phase ofsaid rotational movement the two spring means act in parallel.
 2. Arotary coupling device as claimed in claim 1 wherein in the said firstset of windows the driven plate window has the greatest circumferentiallength, and the floating plate window the smallest circumferentiallength, and in the second set of windows the hub flange window has thegreatest circumferential length and the floating plate window thesmallest circumferential length.
 3. A rotary coupling device as claimedin claim 2 wherein the circumferential lengths of the floating platewindows in said first set and said second set of windows aresubstantially the same.
 4. A rotary coupling device as claimed in claim2, which is in the "at rest" state, wherein for said first set of springwindows the respective window edges are in alignment at a leadingcircumferential end of said first set, and for said second set of springwindows the respective window edges are in alignment at a trailingcircumferential end of said second set, whereas the terms leading andtrailing refer to the direction of rotation of the driven plate relativeto the hub flange during the drive condition of the coupling devicewhile in use.
 5. A rotary coupling device as claimed in claim 2, whereinfor said first set of spring windows the circumferential length of thedriven plate window exceeds the circumferential length of the floatingplate window by a distance equivalent to a first desired angle ofrelative rotation, and for the second set of spring windows thecircumferential length of the hub flange windows exceeds thecircumferential length of the floating plate window by a distance alsoequivalent to said first desired angle of rotation.
 6. A rotary couplingdevice as claimed in claim 5 wherein for said first set of springwindows the circumferential length of the hub flange window exceeds thecircumferential length of the floating plate window by a distanceequivalent to a second desired angle of relative rotation and which issmaller than said first desired angle of rotation, and for the secondset of spring windows the circumferential length of the driven platewindow exceeds the circumferential length of the floating plate windowby a distance also equivalent to said second desired angle of rotation.7. A rotary coupling as claimed in claim 1 in which there are fourspring means in four sets of spring windows, there being two sets ofsaid first set of spring windows which are arranged diametricallyopposite each other, and two sets of said second set of spring windowsalso diametrically opposite each other.
 8. A rotary coupling device asclaimed in claim 1 wherein the coupling device is a friction clutchdriven plate for a vehicle friction clutch, and the driven platecomprises a facing carrier plate arranged to one axial side of the hubflange and to which a friction facing is secured, and a side plate isarranged on the other axial side of the hub flange and is fastened tothe carrier plate by stop pins which pass through apertures in the hubflange to limit the angular rotation between the hub flange and thedriven plate, and there are also provided two floating plates which arelocated one on each side of the hub flange between said flange and arespective one of the carrier and side plates, and which also haveapertures therein to accommodate the stop pins.
 9. A rotary couplingdevice as claimed in claim 1, wherein the coupling device is a splitflywheel, and said driven plate forms part of a first flywheelarrangement and the hub forms part of a second flywheel arrangementspaced axially from the first flywheel arrangement.
 10. A frictionclutch driven plate as claimed in claim 8, wherein in the "at rest"position each stop pin passes through a respective aperture in the hubflange so that from the "at rest" position the facing carrier plate canrotate further in one direction of rotation than in the other directionof rotation.